Pulse Flow Update:
In spring 2014, additional water was released into the Colorado River in a “pulse flow” to simulate natural floods. Even though this flow is a small fraction of the historical spring flow, it was visible in a Landsat 8 image. The water appears as a thin dark line winding through the tan background of the dry floodplain. The dark green squares surrounding the river are farm fields. The Colorado River has only rarely reached its natural delta in Mexico at the Sea of Cortez (or Gulf of California) since 1960, due to numerous dams and diversions.
Water provided by the Minute 319 agreement between the United States and Mexico is intended to promote riparian habitat restoration along the river in its delta.
USGS crews continue to work on this collaborative effort and updates will be reported here as they happen. This video (Minute 319 Pulse Flow) provides a unique perspective of one USGS teams efforts before and after the pulse flow.
A Resource Run Dry
The now-dry Colorado River delta was once a thriving wetland ecosystem, teeming with wildlife. It was a treasured resource shared by both the U.S. and Mexico where water and sediment delivered from the Colorado River reached the Gulf of California. A century ago, the Colorado River delta was even navigable by large boats. Today, upstream diversions and dams in both countries control the Colorado River’s flow, and little to no water is released into the channel downstream of Morelos Dam in most years.
An Agreement Across Borders
Recognizing the challenges facing the Colorado River Basin, including a 14-year period of historic drought, Minute 319 was executed on Nov. 20, 2012. It provides measures to enhance sharing of water supplies, permit Mexico to defer delivery of some of its allotted water in the United States, facilitate investment in Mexico’s water infrastructure, and measure the ecosystem effects of an experimental environmental pulse flow into the reach below Morelos Dam.
Bi-National Effort to Potentially Restore the Resource
In order to assist and inform future bi-national cooperative efforts as both countries work together protect resources on both sides of the border, a large pulse of water is being released into the former delta of the Colorado River along the U.S.-Mexico border.
U.S. Geological Survey scientists are studying the effects of this study on the environment as part of a historic, bi-national collaborative effort. This pulse flow and the need to study its effects were agreed to as part of the recently adopted Minute 319 to the 1944 US-Mexico Water Treaty.
This engineered release of water is the culmination of years of negotiations led by the U.S. and Mexican Sections of the International Boundary and Water Commission in partnership with the Department of the Interior, in conjunction with the seven U.S. Colorado River Basin states, Mexican government agencies and a wide array of municipal agencies, non-governmental organizations and universities from both the U.S. and Mexico. The release of water began on March 24 and will continue for about eight weeks, with the rate of release peaking on March 27. Over this period of time, 105,392 acre feet of water will be released, a volume that would fill about 52,000 Olympic sized swimming pools.
Studying the Flow
Minute 319 to the 1944 US-Mexico Water Treaty calls for studying the hydrologic and biologic effects of the pulse flow. Scientists from the USGS, the University of Arizona, the Universidad Autónoma de Baja California (UABC), Pronatura Noroeste, the Sonoran Institute, the Bureau of Reclamation and other institutions are conducting water monitoring and research along a 24-mile long river segment of the Colorado River where one bank is in Arizona and the other is in Baja California, Mexico. Experts will monitor where the pulsed water flows, track sediment transport and evaluate plant and wildlife response.
Research will focus on how the water moves through the Colorado River channel, how the pulse changes as it moves downstream and infiltrates through the streambed into the groundwater, water salinity levels, and the patterns of new vegetation establishment.
Will the Vegetation Grow?
The successful establishment of native seedlings is dependent on a number of aspects of streamflow, including: the magnitude and timing of peak flows; the rate at which water levels recede; and the availability of shallow groundwater. Studying all these factors will provide an understanding of why vegetation is able to thrive in some areas and not in others. The spread of seeds and new growth will be measured at 22 study sites along the river. Previous unintentional high flows in the mid-1980s and the 1990s promoted the germination and establishment of cottonwood and willow trees.
Other factors that may affect streamflow patterns and vegetation response include sediment transport and changes to the topography of the landscape. The pulse flow will be introduced into a channel with a sand bed, and an unknown amount of sand and mud will be redistributed within the channel and floodplain by this flow. Scientists will study how much sediment is moved and how much of the channel scours or fills with sediment. This information is essential in developing new tools to predict effects of future pulse flows, should they occur.
Eyes in the Sky
Satellite and aircraft-based imagery will be collected along the length of the Colorado River delta, including areas downstream of the U.S.-Mexico border, and will compliment on-the-ground observations. These images will be used to compare the distribution and density of the delta’s vegetation before and after the pulse flow and document the extent of flow inundation. LiDaR will be used to produce high-resolution digital elevation models that will help quantify changes to channel and floodplain topography.
Hope for the future?
“These results will not only help inform decisions about potential future flows, but will also advance cooperative management efforts to improve the health of the delta region in both the U.S. and Mexico,” said Suzette Kimball, Acting USGS Director.